Conventional computer aided navigation devices may contain a map database that describes the geometry, name and other information regarding roads in a geographic area. However, the map database may be inaccurate. Such inaccuracies result from any of several sources. One source of inaccuracy is that the map database itself contains an error. Another source of inaccuracy is that a temporary portion of the road is built around the regular road surface, such as may occur during construction or that the road has been permanently repositioned. Another source of inaccuracy is that the map database is incomplete. For example, the map database may not reflect the fact that a road that appears to intersect another road actually uses a diamond, cloverleaf or other form of off ramp to do so, and that direct access (i.e. without the use of one of the ramps) from one of the two intersecting roads to the other intersecting road is not possible. Another incomplete description may occur when the layout of the roadway cannot be accurately described due to limitations of the map database. For example, a single freeway off ramp that forks, with one fork appearing like a lane of a diamond-shaped off ramp and the other fork heading under the intersecting roadway may not be describable in the terms that the map database uses. Another example is a roadway that travels over or under another roadway rather than intersecting it, making it impossible to turn from one roadway directly onto to another. Because conventional map databases may not include altitude data, determining that direct turns are not possible is not itself possible using some conventional map databases.
Traveling around to check the accuracy of a map database, and surveying any differences would be prohibitively expensive and time consuming. It would be desirable to record the Global Positioning System (GPS) information received by a computer aided navigation device to detect, and correct for, any such inaccuracies. For example, as an automobile traveled along a ramp that did not appear on a conventional map database, periodically, the GPS coordinates of a navigation device in that automobile could be recorded and used to update the map database. However, a conventional GPS device may have sufficient accuracy to allow updating of a map database in this fashion to be performed with a level of accuracy that would correspond to that of conventional map databases.
What is needed is a system and method that can correct inaccuracies of a map database with reasonable accuracy.